Tubular prostheses such as stents, grafts, and stent-grafts (e.g., stents having an inner and/or outer covering comprising graft material and which may be referred to as covered stents) have been widely used in treating abnormalities in passageways in the human body. In vascular applications, these devices often are used to replace or bypass occluded, diseased or damaged blood vessels such as stenotic or aneurysmal vessels. For example, it is well known to use stent-grafts, which comprise biocompatible graft material (e.g., Dacron® or expanded polytetrafluoroethylene (ePTFE)) supported by a framework (e.g., one or more stent or stent-like structures), to treat or isolate aneurysms. The framework provides mechanical support and the graft material or liner provides a blood barrier.
Aneurysms generally involve abnormal widening of a duct or canal such as a blood vessel and generally appear in the form of a sac formed by the abnormal dilation of the duct or vessel wall. The abnormally dilated wall typically is weakened and susceptible to rupture. Aneurysms can occur in blood vessels such as in the abdominal aorta where the aneurysm generally extends below the renal arteries distal to or toward the iliac arteries.
In treating an aneurysm with a stent-graft, the stent-graft typically is placed so that one end of the stent-graft is situated proximal to or upstream of the diseased portion of the vessel and the other end of the stent-graft is situated distal to or downstream of the diseased portion of the vessel. In this manner, the stent-graft extends through and spans the aneurysmal sac and extends beyond the proximal and distal ends thereof to replace or bypass the dilated wall. The graft material typically forms a blood impervious lumen to facilitate endovascular exclusion of the aneurysm.
Such prostheses can be implanted in an open surgical procedure or with a minimally invasive endovascular approach. Minimally invasive endovascular stent-graft use is preferred by many physicians over traditional open surgery techniques where the diseased vessel is surgically opened, and a graft is sutured into position bypassing the aneurysm. The endovascular approach, which has been used to deliver stents, grafts, and stent-grafts, generally involves cutting through the skin to access a lumen of the vasculature. Alternatively, lumenar or vascular access may be achieved percutaneously via successive dilation at a less traumatic entry point. Once access is achieved, the stent-graft can be routed through the vasculature to the target site. For example, a stent-graft delivery catheter loaded with a stent-graft can be percutaneously introduced into the vasculature (e.g., into a femoral artery) and the stent-graft delivered endovascularly across the aneurysm where it is deployed.
When using a balloon expandable stent-graft, balloon catheters generally are used to expand the stent-graft after it is positioned at the target site. When, however, a self-expanding stent-graft is used, the stent-graft generally is radially compressed or folded and placed at the distal end of a sheath or delivery catheter and self expands upon retraction or removal of the sheath at the target site. More specifically, a delivery catheter having coaxial inner and outer tubes arranged for relative axial movement therebetween can be used and loaded with a compressed self-expanding stent-graft. The stent-graft is positioned within the distal end of the outer tube (sheath) and in front of a stop fixed to the distal end of the inner tube. Regarding proximal and distal positions referenced herein, the proximal end of a prosthesis (e.g., stent-graft) is the end closest to the heart (by way of blood flow path) whereas the distal end is the end furthest away from the heart during deployment. In contrast, the distal end of a catheter is usually identified as the end that is farthest from the operator, while the proximal end of the catheter is the end nearest the operator (handle). Once the catheter is positioned for deployment of the stent-graft at the target site, the inner tube is held stationary and the outer tube (sheath) withdrawn so that the stent-graft is gradually exposed and expands. An exemplary stent-graft delivery system is described in U.S. patent application Publication No. 2004/0093063, which published on May 13, 2004 to Wright et al. and is entitled Controlled Deployment Delivery System, the disclosure of which is hereby incorporated herein in its entirety by reference.
Although the endovascular approach is much less invasive, and usually requires less recovery time and involves less risk of complication as compared to open surgery, there can be concerns with alignment of asymmetric features of various prostheses in relatively complex applications such as one involving branch vessels. Branch vessel techniques have involved the delivery of a main device (e.g., a graft or stent-graft) and then a secondary device (e.g., a graft or stent-graft) through a fenestration or side opening in the main device and into a branch vessel.
The procedure becomes more complicated when more than one branch vessel is treated. One example is when an aortic abdominal aneurysm is to be treated and its proximal neck is diseased or damaged to the extent that it cannot support a patent connection with a prosthesis. In this case, grafts or stent-grafts have been provided with fenestrations or openings formed in their side wall below a proximal portion thereof. The fenestrations or openings are to be aligned with the renal arteries and the proximal portion is secured to the aortic wall above the renal arteries.
To ensure alignment of the prostheses fenestrations and branch vessels, current techniques involve placing guidewires through each fenestration and branch vessel (e.g., artery) prior to releasing the main device or prosthesis. This involves manipulation of multiple wires in the aorta at the same time, while the delivery system and stent-graft are still in the aorta. In addition, an angiographic catheter, which may have been used to provide detection of the branch vessels and preliminary prosthesis positioning, may still be in the aorta. Not only is there risk of entanglement of these components, a standard off the shelf prosthesis with pre-formed fenestrations may not properly align with the branch vessels due to differences in anatomy from one patient to another. A custom prostheses having preformed fenestrations or openings based on a patient's CAT scans also is not free from risk. A custom prosthesis is still subject to a surgeon's interpretation of the scan and may not result in the desired anatomical fit. Further, relatively stiff catheters are used to deliver grafts and stent-grafts and these catheters can change or distort the path or shape of the vessel (e.g., artery) in which they are introduced. When the vessel is reshaped by an outside force such as a stiff catheter, even a custom designed prosthesis may not properly align with the branch vessels.
U.S. Pat. No. 5,617,878 to Taheri discloses a method comprising interposition of a graft at or around the intersection of major arteries and thereafter, use of intravenous ultrasound or angiogram to visualize and measure the point on the graft where the arterial intersection occurs. A laser or cautery device is then interposed within the graft and used to create an opening in the graft wall at the point of the intersection. A stent is then interposed within the graft and through the created opening of the intersecting artery.
U.S. patent application Ser. No. 11/276,512 to Marilla, entitled Multiple Branch Tubular Prosthesis and Methods, filed Mar. 3, 2006, and co-owned by the assignee of the present application, discloses positioning in an endovascular prosthesis an imaging catheter (intravenous ultrasound device (IVUS)) having a device to form an opening in the side wall of the prosthesis. The imaging catheter detects an area of the prosthesis that is adjacent to a branch passageway (e.g., a renal artery), which branches from the main passageway in which the prosthesis has been deployed. The imaging catheter opening forming device is manipulated or advanced to form an opening in that area of the prosthesis to provide access to the branch passageway. The imaging catheter also can include a guidewire that can be advanced through the opening.
Generally speaking, one challenge in prosthesis (e.g., stent-graft) delivery/placement in the vicinity of one or more branch vessels is identifying and locating the position of branch vessels (e.g., arteries). For example, this challenge exists whether the distal end of the prosthesis is to be positioned below or above the renal arteries. Although fluoroscopy has been used to identify branch vessels such as the renal arteries for assisting in prosthesis positioning, there remain challenges with this approach. More specifically, fluoroscopy has been used to observe real time X-ray images of the openings within cardiovascular structures such as the renal arteries during a stent-graft procedure. This approach requires one to administer a radiopaque substance, which generally is referred to as a contrast medium, agent or dye, into the patient so that it reaches the area to be visualized (e.g., the renal arteries). A catheter can be introduced through the femoral artery in the groin of the patient and endovascularly advanced to the vicinity of the renals. The fluoroscopic images of the transient contrast agent in the blood, which can be still images or real time motion images, allow two-dimensional visualization of the location of the renals.
The use of X-rays, however, requires that the potential risks from a procedure be carefully balanced with the benefits of the procedure to the patient. While physicians always try to use low dose rates during fluoroscopy, the length of a procedure may be such that it results in a relatively high absorbed dose to the patient. Patients who cannot tolerate contrast enhanced imaging or physicians who must reduce radiation exposure need an alternative approach for defining the vessel configuration and branch vessel location.
There remains a need to develop and/or improve prosthesis deployment apparatus and methods for endoluminal or endovascular applications.